The new generator is almost complete.
It can generate IOR and Specular maps from 3 different map inputs so far.
#1 Cross Polarization Specular Scan
This is the best solution, your Corona render will have identical reflections to the real world cross polarized specular map.
This is the result
#2 Normal Map
This is the second best solution. If you don't have a cross polarized specular map, you can use this one.
You can use any existing normal map. It will generate a IOR / Specular map based on the normal map height strength.
This was initially Jurajs idea, and Ondra gave me some pro tips. So this generator would not exist if not for them!
This is the result
#3 Reflection Level
This is the shittiest last solution.
It will convert old reflection level maps to IOR/Specular. This will give you the same look as you had before, but it will not clamp fresnel.
Since the new generator also generate specular maps, we get real world reflection behavior in Unreal 4!
When everything is road tested and tweaked, I will compile them as 3 LUTs.